During interconnection of two sections of pipe on a drill string, it is necessary that the correct torque be maintained for the interconnection. If this interconnection is not effected properly, failure of the drill string may result. For example, if the two sections of pipe are torqued to a value that exceeds the manufacturers specifications, it is possible that any or all of the following conditions can occur:
SWELLED BOXES PA1 GALLED THREADS PA1 STRIPPED THREADS PA1 STRESS CRACK IN PIN OR BOX
If the torque is at value that is lower than that specified by the manufacturer, it is possible that a proper seal will not be provided. This seal is necessary since pressurized drilling fluids flow through the drill string and could possibly flow around the interconnection and through the side of the drill string if the seal is not present. This may result in a "wash out" of the pipe dope used on the threads when the joint is first made up. If this pipe dope is removed, the action of drilling can cause an overtorque condition resulting in the above conditions. It can also cause the threads to seize together making the breaking of the joint impossible.
During the torquing operation, a Tong is placed around the interconnection after the interconnection is hand tightened. The Tong is essentially a moment arm that is disposed at right angles to the rotational axis of the connection. By disposing a force at right angles to the Tong at a predetermined distance from the connection, a rotational force, or torque, will result at the connection utilizing the Tong as the moment arm. The torque is a combination of the force applied to the Tong and the length thereof which is measured in foot-pounds (ft-lbs). A cable attached to a pneumatically controlled winch is attached to the Tong to provide a manually controlled pulling force. The operator is referred to as a "driller" and he is primarily responsible for the torquing operation. In present systems, a gauge is attached between the cable and the Tong to provide a measurement of pulling force on the face thereof. However, these gauges are susceptible to high inaccuracies and lack the ability to average the torque out over a period of time as they measure the instantaneous torque that is applied. In addition, it is necessary to maintain a 90.degree. angle between the cable attached to the winch and the Tong such that the gauge reading can be directly correlated with torque. If the angle is not maintained perpendicular, inaccuracies may result. Because of this, the driller must pay very close attention to the gauge while also paying attention to his machinery and the people assisting him in the torquing operation. This presents serious disadvantages in that there are many potential hazards that the driller must be aware of.
During the torquing operation, the driller regulates the flow of pressurized air to an air clutch that is attached to the winch to provide the requisite pulling force. This allows the driller to both regulate the rate at which the torque is applied and also the maximum force that is applied to the Tong. In placing the Tong about the interconnection, the driller anticipates the amount of rotation such that the Tong will coincide with the moment arm when the proper torque is reached. However, this is at best a "hit and miss" operation. Depending upon the conditions of the threads, more or less rotation may be required in order to achieve a desired torque reading. Since the only indication of torque that the driller has is the gauge reading which is only an indication of the liner force on the cable, angular deviations between the cable and the Tong are no way accounted for and, as such, may result in damage to the joint.
In view of the above disadvantages with present torque monitoring systems, there exists a need for a torque monitoring apparatus that decreases the probability of overtorquing and undertorquing due to the angular deviations between the cable and the Tong.